An Eco-Friendly Scheme for the Cross-Linked PolybutadieneElastomer via Thiol−Ene and Diels−Alder Click ChemistryJing Bai, Hui Li, Zixing Shi,* and Jie Yin

School of Chemistry & Chemical Engineering, State Key Laboratory of Metal Matrix Composite Materials and Shanghai Key Lab ofElectrical Insulation and Thermal Ageing, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China

*S Supporting Information

ABSTRACT: We reported a novel method of producing the cross-linked polybutadiene elastomer which could be thermallyrecycled like the plastic materials without the sacrifice of functional utility. The commercial polybutadiene was first attached withfuran via thiol−ene reaction, and the cross-linked network was then built via Diels−Alder click reaction between thebismaleimide and attached furan groups from polybutadiene. The obtained polymer had good solvent resistance from ambienttemperature to 100 °C. The mechanical properties of modified polybutadiene could be tailored by the amount of attached furanand the ratio of furan to bismaleimide. Furthermore, the dynamic cross-linked polybutadiene had good thermally remolded andself-healing behaviors. By this method, the dynamic cross-linked polybutadiene could be recycled to use in a sustainable way.Concerning all the raw materials were available in large quantities without tedious and multistep synthetic routes, this workdemonstrated the high performance recycling solution to the commercial cross-linked polybutadiene, which might be applied inindustry in relatively short time.

■ INTRODUCTIONNowadays, rubbers have been widely used in various fields,including transport vehicles, sports equipment, buildingmaterials, etc. The consumer demands drive the increasedproduction of the rubber materials, and people have producedabout 11 million tons of rubber in 2013. However, thediscarded or damaged rubber cannot be reprocessed again toproduce new rubber products due to its cross-linking structurewhere all the chains of rubber lose their ability of movement, sothat they can only thermally decompose at high temperature.1

Therefore, it is still difficult to break down the thermodynami-cally irreversible network of the rubber to produce a valuablerecycled material. Consequently, this huge amount of wasterubber material is an environmental problem2 of great concern.By now, a widely used way to treat this cross-linked rubber is toblend ground discarded rubber with virgin material followed bythe cross-linking reaction.1,3 But the main disadvantage of thisrecycling technique is bad adhesion between the crumb andmatrix of virgin rubber material due to poor interfacial action.1

As a result, it is highly desirable to design the reversibledynamic cross-linked rubber with cross-linked structuremaintained at operating temperature and unlocked at high

temperature to liberate the cross-linked chains of the rubber. Inthis sustainable way, the cross-linked rubber can be remoldedjust like plastic materials, and people can reduce theconsumption of petroleum-based raw materials and save thenonrenewable resources by recycling the rubber. Today, todesign the cross-linked resins in the dynamic way4 has becomea hot research area,5,6 and people have designed several kinds ofnew recyclable cross-linked epoxy7−9 and polyurethane10−12

materials based on Diels−Alder click reaction in thelab.7−10,13−16 The Diels−Alder (DA) click reaction canundergo between a conjugated diene and a dienophile resultingin a cyclohexene derivative at room temperature to about 100°C.17 In the meantime, the cross-linked DA adducts canundergo a reverse reaction typically at temperatures above 120°C to produce the raw materials which is known as a retro-Diels−Alder (rDA) reaction.18 For example, the Sun researchgroup has designed a new kind of polyurethane with maleimidependant chain extender and the furan cross-linkers;10 dynamic

Received: February 23, 2015Revised: April 20, 2015Published: May 15, 2015

Article

pubs.acs.org/Macromolecules

© 2015 American Chemical Society 3539 DOI: 10.1021/acs.macromol.5b00389Macromolecules 2015, 48, 3539−3546

pubs.acs.org/Macromoleculeshttp://dx.doi.org/10.1021/acs.macromol.5b00389

cross-linked polyurethane with good mechanical properties wasobtained, and it could be recycled at high temperatureeffectively. However, up to now, few research works24 havebeen reported on the commercial available olefin rubber withgood recycling ability. Unlike the cross-linked epoxy andpolyurethane resins where considerable molecular-selectionflexibility can allow great freedom to design dynamic cross-linked network, there are almost no active bonding sites forrubber to attach functional groups for forming dynamic cross-linking network. Only double bonds, which are used as anchorfor the cross-linked network, can be selected for chemicalmodification.19,20 Inspired by the chemical reactivity ofdoubling bonds (ene) toward sulfur derivative (thiol), wemodify the chains of rubber through the addition reactionbetween thiol and vinyl groups, also called thiol−ene clickreaction.21,22 The highly efficient reaction between CC andthiol groups under UV irradiation can proceed in mildconditions without the protection of chemical inertnessatmosphere.23 In this paper, we first attached the furan groupsonto the chains of olefin elastomer via thiol−ene click reaction,and then the modified rubber was cross-linked to form thenetwork in the presence of bismaleimide. By this way, the cross-linked olefin elastomer has dynamic cross-linked network.

The primary novelties for this paper include (1) expandingthe thermally reversible cross-linked structure based on the DA-reaction into the commonly used elastomer materials, (2) thecross-linked elastomer could be easily remolded to producenew products, and (3) properties of the cross-linked networkcould be tailored by adjusting the grafting ratio of furan groups(RF) and the ratio of furan to maleimide (RFM). Therefore,the comprehensive properties can be designed with greatfreedom to meet the various requirements in application,overcoming the shortcoming that improving the environmentalsuitability of materials comes with a sacrifice in material otherproperties.

■ EXPERIMENTAL SECTIONMaterials. Toluene was purchased from Sinopharm Chemical

Reagent Co., Ltd. Bismaleimide was purchased from TCI ChemicalCO., Ltd. Polybutadiene (PB) (Mw ∼ 200 000) was purchased fromSigma-Aldrich. Furfuryl mercaptan was purchased from J&K ScientificLtd. All the reagents were used as received.

Chemical Modification of Polybutadiene with Furfuryl Mercap-tan (PB-Fu). Polybutadiene, furfuryl mercaptan, and the photoinitiatorI907 were dissolved in toluene. The addition of furan groups waschanged according to the double bond content of PB chain. Take thesample PB-10Fu for example; the addition of furfuryl mercaptan was

Scheme 1. Reaction Process of the Preparation of the Recyclable Rubber System

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10% of the molar of the double bond on PB chain, and the sampleswere named according to the addition of the furan groups. The recipeof it was as follow: 2 g of PB, 0.4229 g of furfuryl mercaptan, and atrace amount of photoinitiator I907 were dissolved in 20 mL oftoluene and formed a homogeneous solution. Then the solution wasirradiated with UV light for 12 h and magnetically stirred at roomtemperature. Modified PB with different grafting molar ratio of furanwere obtained including 10%, 12%, 14%, 16%, 18%, 20%, and 30%.The recipes for different samples are shown in Table S2. (It wasproved with elemental analysis that the branch ratio of the furangroups was almost the same as the addition of furfuryl mercaptan asshown in Table S3.)Preparation of the Films. Bismaleimide was added into the PB-Fu

solution. After homogeneous mixing, the solution was cast onto glassplates and dried in an air oven at 100 °C for 12 h with different molarratio of bismaleimide and furan groups which had been added to thesystem on the previous step. Two important properties of cross-linkedPB rubber, including the cross-linking degree and mechanicalproperties, could be tuned by adjusting two parameters: the additionratio of furan group to the double bonds on PB chains (RF) and theratio of furan to maleimide (RFM). Two independent cross-linkedsystems were designed. One was the PB-FM system in which RF waschanged and RFM was fixed at 1:1; the other was the PB-3F systemwhere RFM was varied and RF was fixed at 30%. The recipes fordifferent samples for these two series are shown in Tables S4 and S5.Measurements. 1H NMR spectra were carried out on a Varian

Mercury Plus 400 MHz instrument with CDCl3 as the solvent andtetramethylsilane (TMS) as an internal standard at room temperature.Fourier transform infrared (FTIR) spectra measurements wererecorded on a Spectrum 100 Fourier transformation infraredabsorption spectrometer (PerkinElmer, Inc., Waltham, MA) from3200 to 800 cm−1 at a resolution of 4 cm−1. The samples wereprepared by dropping the solution onto KBr films, and 64 scans at aresolution of 2 cm−1 were used to record the spectra. TM-AFMmeasurements were carried out in a SII Nanonavi E-sweep underambient conditions, and the morphology of the samples was examinedby tapping-mode atomic force microscopy (TM-AFM). The measure-ments were performed using commercial Si cantilevers with a nominalspring constant and resonance frequency at about 40 N/m and 300kHz, respectively (AFM Probes, NSC11). The dynamic mechanicaltests were carried out on a (DMTA) (TA Q800, TA Instruments,USA) under the temperature range from 153 to 393 K. The frequencyis 1.0 Hz, and the heating rate is 10 K/min. The specimens have widthof 4 mm and length of 30 mm. Differential scanning calorimetry(DSC) analysis was carried out with DSC 6200 (Seiko InstrumentInc.) at a heating rate of 20 K/min from 323 to 573 K and nitrogenflow rate of 50 mL/min; about 5 mg samples were sealed in aluminumhermetic pans and lids for the tests. The tensile property of the filmswas measured with an Instron 4465 instrument at room temperaturewith a humidity of about 30% at a crosshead speed of 100 mm/min.Dumbbell specimens with width of 4 mm and length of 30 mm werecut from the cast films. Data analyses were based on five

measurements on each sample performed at the same conditions.The self-healing property of the material was evaluated by POManalysis. A crack on the polymer film was observed on polarizingoptical microscopy (LEICA DM LP) equipped with temperature-programmed heating stage (TMS 94). Rheology experiments wereperformed with 8 mm plate−plate geometry on a BOHLIN GEMINIrheometer in the oscillating shear mode, and the scanning temperaturewas from 80 to 170 °C with the cross-linked PB rubber in the elasticstate. The sample thickness was set to a fixed value of 0.3 mm, and aconstant deformation of 0.1% shear strain at a frequency of 0.15 Hzwas used. Elemental analysis was carried on a Vario-EL Cube(Elementar). The gel fraction and swelling ratio of samples weredetermined by soaking the sample in toluene for 48 h at roomtemperature. After that, the insoluble polymer was dried at 80 °C tothe constant weight (W3). The original weight of the sample wasexpressed as W1. The weight of the swollen sample immediately takenout of toluene was signed as W2. Therefore, the gel fraction (GF) andthe swelling ratio (SR) were calculated according to the formulas

= × =W W W WGF / 100%; SR /3 1 2 1

■ RESULTS AND DISCUSSIONIn this paper, a typical example of olefin-based rubber, thebutadiene elastomer (PB), was selected for investigation. Thegeneral modification and cross-linking reaction are shown inScheme 1. We first attached the furan group onto the chains ofthe butadiene based rubber via thiol−ene reaction, and then thefuran-modified PB (PB-Fu) was further cross-linked withbismalemide based on the DA reaction on the solution method.

Structure Analysis of Furan Modified PB by NMR andFTIR. The structure of the furan functional PB was firstcharacterized by 1H NMR. As shown in Figure S1A, the peaksat δ = 6.34, 6.28, and 7.35 ppm were assigned to the protons a,b, and c of the furan ring separately. The peak at δ = 3.68 wasthe signal of the proton connecting to the carbon atombetween furan ring and sulfur. The signal between 5.30 and5.50 belonged to the proton connecting to double bonds. Allthe samples with different grafting ratio of furan groupspossessed similar 1H NMR with different integrals. Two peak(δ) areas at 3.68 and between 5.30 and 5.50 were used tocalculate the grafting ratio of furan groups. The detailedmethod and analysis are shown in the Supporting Information,and its results are shown in Table S1. It was found that theexperimental value was close to the theoretical value for thegrafting ratio, which proved that the modification of thepolybutadiene with designed amounts of furan groups based onthiol−ene click reaction were highly efficient. And the data aresummarized in Table S1. FT-IR spectra were further used tocharacterize the furan modified PB. Compared with PB, PB-Fu

Figure 1. Gel fraction and the swelling ratio of the PB-FM (A) and PB-3F (B) series.

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exhibited new characteristic absorption peaks at 1240 and 1148cm−1, which was closely related to the furan group. Therefore,based on these spectral analyses, it was verified that furangroups have been successfully grafted to the chain of PB viathiol−ene reaction.Solubility Behavior for the Cross-Linked Elastomer.

Since the linear and cross-linked structures were quite differentin their solubility, change in solubility of the furan modified PBelastomer in toluene could be used as the first direct evidenceto prove that the modified polybutadiene was actually cross-linked via DA reaction between bismaleimide and furan groupsto form tridimensional polymer networks. As shown in Scheme1, it was observed that the furan-modified PB showed goodsolubility in toluene. However, after reacting with bismaleimide,the PB could only swell in the toluene. Such comparisonproved that the PB rubber was successfully cross-linked withthe presence of bismaleimide. Meanwhile, the cross-linkingdegree of PB rubber could be investigated by its gel fraction andswelling ratio. As shown in Figure 1A for the PB-FM system, itwas observed that the gel fraction and swelling degree were77.3% and 3.38, respectively, as RF was about 10% (PB-FM-10). With increasing RF up to 20% (PB-FM-20), the gelfraction for the cross-linked PB rubber was increased to 99.6%and its swelling ratio was decreased to 2.30. For the PB-3Fsystem, it was also found that increasing RFM could increasethe gel fraction and decrease the swelling ratio. The resultsfrom the analysis of solubility showed that the cross-linkingdegree for PB elastomer was easily adjusted by changing RFand RFM, which was convenient for us to investigatemechanical properties of the cross-linked PB rubber by tailoringthe amount of grafted furan and bismaleimide.Analysis of Morphology for the Cross-Linked PB

Elastomer. AFM could easily detect the hard and soft phasesbased on their different hardness. Commonly, cantileveroscillation acting on hard surface lost energy and generatedsmaller phase contrast. Hence, the hard phase was the brighterregion reflecting in the phase image. On the contrary, the softdomain was reflected as the dark region. In this system, thecross-linking domains based on the DA reaction betweenbismaleimide and furan were hard phase. Therefore, thebrighter domains correspond to the cross-linking domains(FM phase), and the darker domains correspond to the part ofpolybutadiene (PB phase). In order to understand the effects ofRF and RFM on microstructural morphology, AFM phaseimages were taken on these two systems. As shown in Figure 2

for the PB-FM system, only bright spherical particle domainsattributed to the hard phase (the cross-linking domains) wereobserved, and the hard domains protruded from the PB phase.The diameter of particle was about 30−50 nm for PB-10FM.With increasing RF content, the size of particles was graduallydecreased, and the boundary of particles become obscure withmore homogeneous morphology obtained.The morphology of the PB-3F system is shown in Figure 3.

As the RFM was below 40%, only soft phase almost covered the

whole surface without obvious phase separation; with furtherincreasing RFM, the hard phase gradually protruded from thesoft phase and phase separation structure was obtained.

Mechanical Properties for the Cross-Linked PB. Figures4A and 4D show the tensile stress versus strain curves at roomtemperature for these two series, and the derived mechanicaldata are summarized in Tables S7 and S8. As shown in Figure4A for PB-FM, it was found that increasing grafting RF from10% to 30% could increase the modulus and decrease theultimate strain for the cross-linked PB. For example, as RF wasincreased from 10% to 30%, the modulus was increased from14.0 to 48.4 MPa, while the ultimate strain was decreased from80.6% to 44.8% with breaking stress shifting around 4.60 MPa.The main reason for this phenomenon was that increasing RFwould lead to increasing cross-linking degree, which finallyresulted in increase in the strength and modulus and decreasein strain. For the PB-3F system, a very interesting phenomenonwould be observed, which was quite different from PB-FM. AsRFM was 10% (PB-3F-10M), the breaking stress and moduluswere 1.92 and 2.0 MPa, which were quite lower than those forPB-FM. However, its ultimate strain was 342.5%, much higherthan that for PB-FM. With further increasing RFM up to 60%(PB-3F-80M), the breaking stress and modulus for wererespectively increased to 5.53 and 45.2 MPa and the ultimatestrain was decreased to 44.6%, and these data were quite similarto those for PB-FM-20. Therefore, difference in the mechanicalbehaviors between PB-FM and PB-3F was decreased withenhancement RFM, which was closely related to their phasestructure. For PB-FM, as shown in the results from AFM, thesoft PB and hard cross-linking domains were observed,indicating that phase separation was found for PB-FM.Therefore, the sample showed the characteristic “strong”elastomer with high modulus and low ultimate strain(

Therefore, the modulus increased greatly, as accompanied bydecreased ultimate strain (

at high temperature around 85 °C, which was associated withthe hard domains from the DA cross-linked structure. Suchphase separation structure was responsible for the strong cross-linked PB (Figure 2). For PB-3F blends, the sample onlypossessed one Tg transition at low temperature of ∼−90 °C asRFM was less than 60%, indicating that only one soft phase wasobtained for the cross-linked PB rubber (Figure 3). However,further increasing bismaleimide content led to the appearanceof the second Tg at higher temperature at ∼90 °C. Such resultsdemonstrated that phase separation happened, and the hardphase related to the bismaleimide cross-linked structure wasformed at higher ratio of furan to bismaleimide (>60%), whichis in agreement with the observation from AFM measurements.The appearance of phase separation with increasing RFM couldbe used as explanation for the transition from “soft” to “strong”elastomer for PB-3F blends with increasing RFM from 10 to100%. Therefore, we could easily design the cross-linked PBrubber by changing the furan grafting ratio and ratio of furan tobismaleimide to meet the corresponding requirements fordifferent application.Remolding Ability and Thermal Recyclability of the

Materials. The thermal recyclability was first demonstrated bythe variation of solubility under different temperature. FigureS3 shows the behavior of solubility as the temperature was setfrom 30 to 130 °C for the sample of PB-FM-20 usingdichlorobenzene as solvent. It was found that the cross-linkedPB could only swell in dichlorobenzene with good solventresistance, even at high temperature of 130 °C. As thetemperature was further increased up to 160 °C(shown inFigure 6E), the cross-linked PB could gradually dissolve intodichlorobenzene to form a clear and transparent solution. Thisphenomena indicated that the disconnection of DA linkage dueto rDA reaction happened on the temperature range between130 and 160 °C, which could finally lead to dissolution of themodified PB rubber. As the solution was cooled down to roomtemperature, the sample changed to a homogeneous andtransparent gel which could be dissolved again at hightemperature, proving that the cross-linked PB rubber had athermal reversible dynamic cross-linked network. DSC wasfurther carried out on the cross-linked sample to verify thetemperature range for the rDA reaction. As demonstrated inFigure S4, the single exothermic peak related to the rDAreaction was observed for all the PB-FM blends, and thereaction starts at 125−130 °C with the peak temperaturelocated at 180−190 °C, which was in agreement with theresults from dissolution tests.For more detailed analysis of the thermally reversible DA

reaction in the network, temperature-dependent rheologyexperiments were performed. As shown in Figure 5A, threeperiods was observed for storage modulus (G′) and lossmodulus (G″). In the first period as the temperature rangedfrom 80 to 120 °C, there was plateau for these two moduluswith G′ higher than G″, indicating that the cross-linkedelastomer was in the high elastic state. In the second period, G′and G″ decreased rapidly as the temperature was increasedfrom 120 to 130 °C, which was attributed to the breakage ofthe network due to retro-DA reaction. In the third period, G′and G″ formed the second plateau when the temperature wasup to 130 °C and G′ was still higher than G″, which meant thatthe de-cross-linked elastomer was still in the elastic state insteadof in the flow state, which was quite different from theconventional materials based on DA cross-linking reaction,where the cross-linked materials suddenly turned into the flow

state, which was difficult to maintain their integrity during theheating process. Such good integrity could be applied in stressrelaxation for the cross-linked PB elastomer. For example, asshown in Figure 5C when the film was stretched at 60 °C(lower than the temperature for the rDA reaction) and thencooled down, the film could return to original length uponheating to 60 °C, showing good shape memory due to thestress produced in the network at high temperature. However,when the same operation was done at 130 °C (above thetemperature for the rDA reaction), the film could not return tooriginal length since the rDA reaction enabled the stressrelaxation in the network and the sample lost the function ofshape memory.In addition, FTIR spectroscopy was observed to analyze the

reversibility of the cross-linking via the thermal reversiblereaction between PB-Fu and bismaleimide in the solid state.The samples were subjected to the following designedtemperature: DA(room temperature)−rDA(150 °C)−DA-(room temperature) (Figure 5B). The obvious change in thisprocess was the intensity of the absorption peak at 1184 and1148 cm−1. Once the sample was heated to 150 °C and kept for3 min, it was observed that intensity of the peak at 1184 cm−1

(II of Figure 5B) decreased, but the intensity of the peak at1148 cm−1 increased. The peak at 1184 cm−1 could be ascribedto the debonding of the DA adduct (C−O−C) via the retro-DA, while the peak at 1148 cm−1 was the absorption peaks offuran rings.13 After slow cooling from 150 to 25 °C, III inFigure 2B showed that the intensities at 1184 and 1148 cm−1

recovered to its original state. This phenomenon attributed tothe regeneration of the DA adduct (C−O−C) and con-sumption of the furan during the cooling process due to the DAreaction. Three cycles of rDA and DA reactions were observed,and similar results were obtained. Therefore, it was concludedthat PB-Fu could be de-cross-linked and re-cross-linked withbismaleimide repeatedly even in the solid state. Therefore, thecross-linked PB rubber could be recycled to produce newsample via hot compression molding at an elevated temper-ature. As shown in Figure 6A, pieces of broken samples werereprocessed under a pressure of 10 MPa for 5 min at 160 °Cand a solid polymer film was re-formed again. Then theremolded film was cut into pieces, and recycling process wasrepeated two times. Figure 6D shows the mechanical properties

Figure 6. (A) Recycling study: the process of heat press polymerpieces into solid film, taking the sample PB-FM-20 for example. (B)Digital images for healing process of BR-Fu-BM. The photo of the filmwith a crack at room temperature and (C) at 150 °C. (D) Stress−strain curves for the pieces shown in Figure 2A (PB-FM-20) throughthree generations of recycling from pieces to films. (E) The sol−gelprocess of the sample PB-FM-20 in dichlorobenzene when thetemperature changed.

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of the remolded elastomer exhibited almost the samemechanical properties even through three generations ofrecycling. Therefore, the cross-linked PB elastomer could berepossessed like plastics materials. In addition, the self-healingproperty of PB-FM was investigated by observing the evolutionof a crack created by a surgical blade. The film with crack wasput on a heating stage, and the temperature was increased at arate of 10 °C/min to induce the consequent healing process.Photographs were taken at different temperatures during theheating process. As shown in Figure 6B, the crack on PB-FMbegan to decrease at about 90 °C and disappeared completelyafter the temperature reached 150 °C, indicating that the cross-linked PB rubber could be self-healed under high temperature.It could be concluded that the self-healing property wasattributed to the DA and rDA reaction between furan groupson polybutadiene chains and bismaleimide as shown in Scheme1. At high temperature, rDA reaction liberates the polymerchain from the network. Meanwhile, the new formed DA bondsconnected the polymer chains together. Therefore, the rDA andDA reaction were responsible for healing the cross-linkedrubber.

■ CONCLUSIONWe prepared the thermally reversible cross-linked polybuta-diene elastomer based on Diels−Alder reaction (DA). In thisway, PB could be thermally recycled like plastic materials toprolong its service life and solve its unrecyclable problem. Thecommercial available PB elastomer was first attached with furanvia thiol−ene click reaction and then cross-linked withbismaleimide via DA. Based on this method, the thermallyreversible cross-linked network was established for PBelastomer with good solvent resistance at ambient temperature.The obtained PB elastomer also could have tunable mechanicalproperties by adjusting the cross-linking degree. For example,for the PB-3F-M system, the cross-linked PB shows low tensilestrength of 1.92 MPa with high strain at break of 342.5% inrelative low cross-linking degree as RFM was 10%. Withincreasing cross-linking degree, the tensile strength wasgradually increased up to 5.59 MPa with reduced strain atbreak to 44.8% as RFM was 100%. More importantly, the newcross-linked elastomer possessed good recyclability and couldbe thermally remolded to produce new sample without obviousnegative effects on its mechanical properties. All in all, this workdemonstrated good eco-friendly recycling solution to thecommercial cross-linked PB elastomer.

■ ASSOCIATED CONTENT*S Supporting InformationFigures S1−S3 and Tables S1−S10. The SupportingInformation is available free of charge on the ACS Publicationswebsite at DOI: 10.1021/acs.macromol.5b00389.

■ AUTHOR INFORMATIONCorresponding Author*E-mail zxshi@sjtu.edu.cn; Fax + 86-21-54747445; Tel + 86-21-54743268 (Z.S.).NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe thank the National Nature Science Foundation of China(No. 51473091) for the support.

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